In recent years, low GWP refrigerant has been developed to reduce the influence of global warming. Although R410A having been typically used exhibits good performance, its global warming potential (GWP) is about 2000. For this reason, R32 whose GWP is about ⅓ of the GWP of R410A has been increasingly used. Although R32 is a refrigerant having physical properties close to those of R410A and exhibiting good performance, the GWP of such refrigerant is about 600. For a lower GWP, fluoropropene-based (HFO-based) refrigerants such as HFO-1234yf have been developed.
However, such refrigerants are high boiling refrigerants, and exhibit low performance. For maintaining performance similar to that of the typical refrigerant, there is a probability of causing many technical issues and increasing the cost.
Thus, a refrigeration cycle apparatus has been proposed, which employs a refrigerant (e.g., HFO-1123) whose global warming potential is low and whose boiling point is low (see Patent Literature 1).
It has been known that HFO-1123 has less influence on the ozone layer because the composition of HFO-1123 contains no chlorine atom, and that HFO-1123 has less influence on global warming and exhibits excellent performance (capacity) because HFO-1123 has a double bond and a shorter life in atmosphere (i.e., HFO-1123 is a low boiling refrigerant). Moreover, HFO-1123 belongs to a category equivalent to rank 2 L (low flammability) of ASHRAE's flammability classification, achieving safety.
Refrigerants such as HC, HFC, HCFO, CFO, and HFO can be mixed with HFO-1123 so that a zeotropic refrigerant mixture partially having advantages of such refrigerants is formed.
It has been known that in a refrigeration cycle apparatus using such a zeotropic refrigerant mixture as a working refrigerant, the composition ratio of circulating refrigerant changes because excess refrigerant containing rich high boiling refrigerant is accumulated as liquid refrigerant in, e.g., an accumulator, and malfunction might be caused due to lowering of performance and an increase in high pressure (see Patent Literature 2).